First of all, count the possibilities remaining in row 7. Five values are already filled in. The only remaining values are {1, 2, 4, 6}.

The values {1, 6} are already filled in in column 2. So r7c2 can only be {2, 4}. But now look at the bottom center 3x3 box, and the "4" at r9c9. Clearly the "4" in row 7 must fit in the bottom center 3x3 box -- that is, in r7c5 or r7c6. So r7c2 can't be a "4", and it must be a "2". dcb